Patent application title: SYSTEMS AND METHODS FOR OPERATING A SURVEILLANCE SYSTEM

Abstract:

A surveillance system can be designed to take advantage of the disruption
of the electromagnetic propagation (EMP) of the radio waves as they
propagate through a spatial volume from a transmitter to a receiver. This
disruption is well-known in the RF field and is usually removed from
becoming a problem in any bidirectional transmission by a variety of
sophisticated techniques. Advantage is taken of the fact that the
presence and/or movement of objects within the range of the transmission
has some effect on the resultant reception. Thus, the disruption of the
EMP between two points can be used to provide surveillance information
over a wide area. In one embodiment, radios are used that can detect and
adapt to changes in the EMP medium and thus are able to adapt to changing
circumstances in real-time.

Claims:

1. A surveillance system comprising:at least one pair of radios, said
radios adapted for communicating with each other across a volume of
space;means for determining when a spatial signature of a particular
communication has changed; andmeans enabled by a determined change for
providing an alert signal outside of said radio pair.

2. The system of claim 1 further comprising:means for processing spatial
signature changes to determine a type of signal to be provided.

3. The system of claim 2 further comprising:a plurality of radio pairs;
andwherein said processing includes spatial signature information from
more than one radio pair.

4. The system of claim 2 wherein said processing further comprises:means
for allowing an operator to input information in real time.

5. The system of claim 1 wherein said radios serve a wireless
communication function in addition to said surveillance.

6. A system for detecting intrusion into an area, said system
comprising:an analyzer for determining when a radio transmission's
electromagnetic propagation (EMP) changes; andan alerting interface for
providing a signal indicating a detected EMP change.

7. The system of claim 6 wherein said analyzer further determines specific
parameters pertaining to said EMP change; andwherein said signal is
provided only when certain specific parameters are determined.

8. The system of claim 7 wherein said analyzer determines said specific
parameters, at least in part, based on differenced of the multi-path
signals from one EMP environment to another EMP environment.

9. The system of claim 8 wherein said analyzer further determining when
said radio transmission's EMP changes once again; and wherein said
alerting interface is further operative for providing another signal
indicating said subsequently detected EMP change.

10. The system of claim 9 wherein said EMP change is based upon
disturbance in electromagnetic propagation from a transmitter to a
receiver.

11. The system of claim 6 wherein said analyzer is part of an adaptive
radio communicating with another radio.

12. A radio surveillance system comprising:at least two EMP adaptive
radios in communication with each other, said radios operative for
reporting spatial signature changes between them; andan interface for
triggering events outside of said radios due to a reported change in a
spatial signature.

13. The system of claim 12 further comprising:a processor for determining
parameters concerning a reported signature change, and wherein said
interface is operative to trigger events based upon said determined
parameters.

14. The system of claim 13 wherein said radios are part of a wireless
communication system.

15. The system of claim 14 further comprising:an object placed in an area
through which RF energy from said radios will pass, said object
selectively changing electromagnetic propagation between said radios on a
relatively permanent basis.

16. A radio comprising:circuitry for reporting electromagnetic propagation
(EMP) changes between said radio and at least one other radio in
communication therewith, said reporting adapted to allow a system
separate from said radio communication to determine when a particular
area undergoes certain environmental changes.

17. The radio of claim 16 wherein said EMP changes are determined by a
change in spatial signature.

18. A method for performing surveillance, said method
comprising:determining when electromagnetic propagation (EMP) changes
between radios that transmit RF energy through a particular space being
monitored; andproviding an alert signal based upon a determined EMP
change.

19. The method of claim 18 further comprising:tailoring said alert signal
dependant upon particular characteristics of said determined EMP change.

20. The method of claim 19 wherein said determining is based upon at least
one of the following: statistics of other EMP changes; time of said EMP
change; a plurality of EMP changes in a particular time period.

21. The method of claim 20 further comprising:rearranging objects in a
area through which RF energy from said radios pass to adjust RF
propagation paths.

Description:

TECHNICAL FIELD

[0001]This disclosure relates to surveillance systems and more
specifically to methods and systems for performing surveillance using
radio communication systems.

BACKGROUND OF THE INVENTION

[0002]Surveillance systems are now commonplace and deployed in a wide
variety of circumstances. Such systems can be as simple as a camera and a
monitor and complex utilizing a combination of pressure sensors, RE and
light beams, sound detectors and the like. Some of the most sophisticated
surveillance systems use an invisible (to the human eye) laser beam
between a source and destination point(s) where detection is based on an
object passing through the beam thereby interrupting the light path from
the sending point and the destination point.

[0003]One disadvantage of such systems is that when the protected
environment changes (such as for example, an object is positioned within
the protected zone) the transmission and reception points must be
adjusted to accommodate the intrusion. By way of example, a problem would
occur when a floor of a building is under surveillance using laser beams
and it is desired to have a guard walk the area from time to time. Care
must be taken to eliminate or redirect the laser beams before the guard
passes.

[0004]The foregoing has outlined rather broadly the features and technical
advantages of the present invention in order that the detailed
description of the invention that follows may be belter understood.
Additional features and advantages of the invention will be described
hereinafter which form the subject of the claims of the invention. It
should be appreciated by those skilled in the art that the conception and
specific embodiment disclosed may be readily utilized as a basis for
modifying or designing other structures for carrying out the same
purposes of the present invention. It should also be realized by those
skilled in the art that such equivalent constructions do not depart from
the spirit and scope of the invention as set forth in the appended
claims. The novel features which are believed to be characteristic of the
invention, both as to its organization and method of operation, together
with further objects and advantages will be better understood from the
following description when considered in connection with the accompanying
figures. It is to be expressly understood, however, that each of the
figures is provided for the purpose of illustration and description only
and is not intended as a definition of the limits of the present
invention.

BRIEF SUMMARY OF THE INVENTION

[0005]A surveillance system can be designed to take advantage of the
disruption of the electromagnetic propagation (EMP) of the radio waves as
they propagate through a spatial volume from a transmitter to a receiver.
This disruption is well-known in the RF field and is usually removed from
becoming a problem in any bidirectional transmission by a variety of
sophisticated techniques. Advantage is taken of the fact that the
presence and/or movement of objects within the range of the transmission
has some effect on the resultant reception. Thus, the disruption of the
EMP between two points can be used to provide surveillance information
over a wide area. In one embodiment, radios are used that can detect and
adapt to changes in the EMP medium and thus are able to adapt to changing
circumstances in real-time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in conjunction
with the accompanying drawing, in which.

[0007]FIG. 1 illustrates an embodiment of a radio surveillance system
using the concepts of the invention;

[0008]FIG. 2 illustrates one embodiment of a changed signature occasioned
by the addition of an object into the transmission space;

[0009]FIG. 3 illustrates one embodiment of the radio function used in the
present invention;

[0010]FIG. 4 illustrates one embodiment of an alert processing system;

[0013]FIG. 7 illustrates one embodiment of an operator interface for an
alert setting; and

[0014]FIG. 8 shows one embodiment of a flow chart of system operation.

GENERAL DESCRIPTION OF THE INVENTION

[0015]Radio surveillance can be performed using either a dedicated system
or in combination with a radio communication system serving another
purpose. For example, in many environments there are several wireless
transmissions already occurring for various purposes. Any one or more of
these can be used to also provide surveillance of the area surrounding
the wireless communication. This is accomplished because the radios
(transmit and receive) of the existing system detect changes in the
environmental conditions within the area, for example refraction or
reflection off of an object causes the EMP to change. These changes need
not be in the direct line between the transmitter and the receiver since
the receiver is subjected to "bounce" and multi-path reception.

[0016]The radio surveillance concepts presented herein have the
fundamental characteristics of laser beam systems but with more
capabilities and enhanced features. In one embodiment, two radios are
used with both radios being transceivers, in that they can both transmit
as well as receive. The example then is a bidirectional detection system
where each EMP transmission in any direction can be different (e.g., the
EMP characteristics for each of the transmitters and receivers are not
necessarily the same). Each radio has a set of spatial signatures of EMP
characteristics for transmitting and receiving. Any object, within the
electromagnetic field impacts the spatial signature and signal
performance and therefore can be detected by the receiving radio(s).

[0017]For example, when a new object moves into the EMP field, each radio
detects a change from the previously received signal and from the initial
channel calibration process and thus a new spatial signature is created.
This change in signature triggers the alert process. It should be clear
that the surveillance area covered by these two radios is much larger
than the point to point laser beam approach, because the radio wave
reflects and refracts to cover and differentiate signals over a wide area
whereas the laser is essentially a beam. Take, for example, a typical
garage door that stops its closing motion when the light beam is broken
by an object (typically a person) moving across the beam. If the person
were to step over the beam the garage door would not stop. If, on the
other hand, the concepts discussed herein were to be used, the radio
detection system would sense the change in the EMP and stop the door.
Note that the using this approach, alignment problems are eliminated and,
if desired, a wider area of coverage could be monitored by the radio
beams.

[0018]Other advantages provided by this invention are 1) that the
invisible electromagnetic field coverage area or pattern could be changed
instantly by moving or adding a reflecting object thereby providing
multiple "baselines" for alerting purposes. For example, the same
deployment of the invention can be used for various partitioning schemes
as can be found in many conference halls with changeable walls; 2) larger
areas can be covered than by other known methods; 3) stationary
non-reflecting or refracting objects (of which there are few can be
easily converted to extend the surveillance area by the addition of small
reflective coatings or coverings; 4) higher powered radios can be used
(either continuously higher powered or in a "burst" mode) to cover larger
areas or to provide greater alerting detail; 5) additional radios can be
added or subtracted to the system, especially those already part of an
otherwise standard communication system, with little or no effort; and 6)
additional radios can be added automatically so as to provide the ability
to auto-discover and auto-add new "zones" to the overall alerting system
and the total region it includes.

[0019]Before beginning a discussion of the operation of one embodiment of
the invention, it might be helpful to review some of the basics of RF
transmission. Any wireless system communication is based on the
propagation of an electromagnetic field (EMF) wave. The antenna is the
interface device or component that converts the electrical signal to EMF
and vice versa. Once converted, the EMF wave propagates freely in the
air. The wave is typically reflected or refracted when it reaches an
obstacle or object and the change from original wave to the reflected or
refracted can therefore be used to identify the range (e.g., from the
echo delay, instantaneous direction from the antenna (pointing
direction), and/or speed of both moving and fixed objects from the
doppler frequency shift). This is the operating principle of Radar.

[0020]Within a building, there are many objects, including walls,
furniture, people, pets, etc. Each reflection can be considered as a
delayed version (or image) of the source signal. Technically, this
environment is referred to as a multi-path environment. Multipath is the
EMF wave propagation phenomenon that results in radio signals' reaching
the receiving antenna by two or more paths. The typical characteristic of
a multi-path environment is "notching" in frequency response of the
medium signal due to cancellation between two signals that have the same
frequency, but different phases or time delay. ("Notching" has the
typical appearance as zeroes.) If there are zeroes, then there likely are
peaks which are difficult to detect. Therefore, the difference in time
delay can be computed from two received signals. In general, multi-path
environments suffer from significantly reduced radio performance and have
been a decades-old challenge. Today, there are three solutions used to
overcome this problem. Solutions to these are discussed below.

[0021]Orthogonal Frequency-Division Multiplexing (OFDM) is a digital
multi-carrier modulation scheme, which uses a large number of
closely-spaced (small narrow-band) orthogonal sub-carriers. OFDM
effectively creates many sub-channels from one large bandwidth channel
with the advantage of being far better able to cope with severe channel
conditions without complex equalization filters. The signal is
transmitted in each sub-channel independently, effectively parallelizing
the transmission media so that communication is not stopped even if some
sub-channels encounter severe interference. The OFDM modulation scheme
works well in the multi-path environment, where signal loss on some
sub-channels from signal cancellation at some frequencies still allows
data to flow on all other sub-channels. In other words, the multi-path
environment may cause some of the sub-channels to be unusable, but will
still allow data to flow on the remaining sub-channels--the communication
link is always active, but not necessarily operating at full capacity.

[0022]OFDM requires that each receiving radio knows which sub-channels
work. Sub-channel discovery can be performed by a protocol between the
sending and receiving radios. For example, either radio can initiate the
necessary sub-channel realignment process to maximize throughput at any
time by sending a unique key code through all sub-channels. The receiving
radio determines which sub-channels have the received data so as to
create the next key code based on the best sub-channel throughput
pattern. The key is then used until next discovery is performed as per
the protocol. The details of the protocol are not discussed here, because
they are irrelevant to this invention. What is important for this
invention is the ability to determine and adapt to a changing environment
using the best sub-channel throughput patterns.

[0023]Direct-Sequence Code Division Multiple Access (DS-CDMA) is a
multiple access scheme based on direct-sequence spread spectrum, by
spreading the signals from/to different transmitters with different
codes. This spread spectrum approach trades bandwidth for signal quality
in noisy environments--thereby increasing transmission rates by N times.
For example, in the IS-95 Cellular standard, N is 128. The relevant
characteristic is managing the multi-path environment with a "Rack"
filter. The function of the "Rack" filter is to present multi-delayed
signal contents of the received signal in the order of time delay. For
example, assuming there are three signal paths from a transmitter to a
receiver, where one of the three paths is the direct path and the other
two are reflected or refracted by walls and/or furniture. In this case
the signal from the direct path will arrive first, because it is the
shortest distance. The other two signals will arrive later. The "Rack"
filter output will display three signals in the order of their
propagation time delay from the transmitter. Should the environment
change, the delay time and signal strength of each signal will also
change. The invention presented herein is based on the principle of
detecting changes in the local environment.

[0024]Multiple-input and multiple-output, or MIMO uses multiple antennas
and signal processing both at the transmitter and receiver to improve the
performance of radio communication systems. MIMO offers advanced control
over the spatial distribution of the electromagnetic field energy which
in turn offers significant increases in data throughput and link range
without additional bandwidth or transmit power. It achieves this by
higher spectral efficiency (more bits per second per Hertz of bandwidth)
and link reliability or diversity (reduced fading). In other words, MIMO
adaptively controls the strength and the direction of the electromagnetic
field. In a multi-path environment, MIMO radios (transceivers) can adapt
and optimize their performance to the local environment. Radio link
adaptation operation involves one radio, R1, at one end of the radio link
which transmits a beacon signal. The receiver, R2, at the other end of
the link processes all received signals from all antennas to achieve the
best single output signal. This is accomplished by changing the
magnitude, A, and phase, φ, of each antenna signal. (The details of
the optimization algorithm for MIMO are not discussed here, because they
are irrelevant to this invention. What is important for this invention is
the ability to determine and adapt to a changing environment using MIMO
signal matching (e.g., signature patterns)). The spatial signatures per
radio link per direction [1], [2] is characterized by a set of As and
φs. The next step is for Radio R2 to respond with a beacon signal
using the spatial signature settings. If R1 determines the channel
signature is significantly different to the one used previously, the
adaptation process continues until the new channel signature is similar
to the previous one. The whole process takes a few micro-seconds.
Communication starts once the channel signature is known.

[0025]In summary, OFDM, DS-CDMA and MIMO technologies, as described above,
have the capability of adapting to changes in the environment. These
technologies can therefore be used together to create a new radio-based
detection system (e.g., either OFDM or CDMA can be coupled with MIMO). Of
particular interest is the ability to incorporate advanced modulation as
well as multiple antennas and signal processing as may already exist in
commercial products for this purpose. For an example, WiFi chips AGN400
[3] from Airgo Networks is based on OFDM and MIMO, while WFB400 [4] from
Qualcomm is based on DS-CDMA and MIMO.

DETAILED DESCRIPTION

[0026]FIG. 1 shows one embodiment 10 of a radio based surveillance system.
System 10 has at least two radios, such as radios 11-1 to 11-N, and an
alert processing station, such as station 14 communicating with the
various radios via data links 16. Note that the alert processing station
can be separate as shown or integrated with one or more radio nodes.
System 10 operation starts from a set of radios that are installed in an
area where surveillance is required. The number of radios required is
based on the size of a three dimensional coverage area (volume),
including areas that actively reflect and/or refract the radio signals
and the level of surveillance detail that is required. Assuming output
power per radio is not increased, large areas and high surveillance
detail requirements will drive up the number of radios. Note that, as
discussed above, these radios can be part of a communication system, such
as a phone system, a wireless data network, etc., that is in place
independent of the surveillance system. It should be noted that the
spatial signature includes spectral information.

[0027]When being used for surveillance purposes, the communication is
always between two radios comprising at least one communication link.
Whether one or multiple communication links are used at-a-time is
immaterial to the operation of the surveillance system as long as each
radio transmits on a regular basis (e.g., every second). The
communication link is based on the electromagnet propagation (EMP)
environment which could consist of direct paths, such as path 12 or/and
indirect paths 13 caused by objects, such as objects 14. The receiver in
this EMP environment (also referred as multi-path environment)
experiences multiple identical input signal patterns separated by time
delays and signal strength magnitudes which can be characterized as a
spatial signature. The EMP environment would be static if all reflective
objects were static. The radio used in this embodiment has self adaptive
capability to the EMP environment changes, so the performance is
acceptable for unrestricted deployment of the radio system. This is
because the EMP environment could be different in any new deployment and
adapts to the on-going spatial changes in the environment from time to
time due to activities within the coverage area.

[0028]FIG. 2 illustrates one embodiment 20 of a changed signature
occasioned by the addition of an object, such as object 21, into the
transmission space. In this example, adaptation of the EMP environment
algorithm involves creating a spatial signature of the EMP environment.
The radio operation is based on the last known spatial signature until
the EMP environment changes, such as occurs when object 21 enters the
picture. When the signature changes a process begins to determine what
caused the change. As will be seen, the change in signature occasioned
when object 21 is encountered triggers a surveillance function. From that
point forward until the next detected signature change the system
processes communications without incident.

[0029]FIG. 3 illustrates one embodiment 30 of the radio control functions
used in the present invention. In this embodiment, the functional diagram
assumes that the radio has a function in addition to the surveillance
function. Such a function can be any wireless communication function
external to the surveillance function. Network interface 32 is used for
this purpose and the interface, working in conjunction with radio
frequency analyzer 33 performs like any typical radio function (e.g.,
modulation and demodulation, up and down frequency shifter, input and
output are radio frequency signals). If the signal modulation is DS-CDMA
or OFDM, then EMP adaptation is possible. For DS-CDMA modulation, the
"Rake" filter in the demodulation would produce a spatial signature in
the form of relative time delays and magnitudes of each multi-path
signals. The relative time delay means the time delay relative to the
first or earliest received signal. For OFDM modulation, the spatial
signature is based on the signal nulling frequencies. (The frequency
response of a multi-path signal would be null at some frequency due to
multi-path signal cancellation.)

[0030]Multi-antenna controller 34 controls multi-path environments. This
is perhaps the most powerful technique for the radio surveillance system.
In this embodiment, the multi-path function uses MIMO technology. The
MIMO technology can be used alone or with any radio types. If the radio
modulation is DS-CDMA or OFDM together with the MIMO, the embodiment
would use the MIMO spatial signature as the prime and DS-CDMA or OFDM
would provide supplementary information. The spatial signature for MIMO
would provide a set of magnitudes and phases for each antenna. For
example, if three antennas are used, the spatial signature has three
magnitudes and three phases.

[0031]Any changes in the spatial signature triggers the immediate sending
of a copy of the new spatial signature from the detected radio to the
alert processing station via a communication link, such as alert process
station interface 35, which could be a part of the radio surveillance
system or an independent communication system. The actual type of alert
communication is immaterial to proper operation, except that high speed
data alert transfer is preferred so as to reduce latency of intrusion
processing. Note that latency can be further reduced by incorporating
some or all the functions of the alert processing into the RF node(s).

[0032]The function of the alert processing station is to determine what
action needs to be taken when a spatial signature change occurs since
each spatial signature change could mean different things under different
conditions. For example, a spatial signature change in a busy office in
the day time likely has little meaning and may be ignored. However, if a
change occurs at night, or at a special location, etc., the change could
be of interest for any number of reasons. If the system has a video
surveillance system, the operator could use the change signal to
automatically adjust the video screen and camera to the location where
the change has occurred. One of the many possible applications of the
alert processing station is to have a programmable GUI interface with
optional selections based on operator/end-user requirements. Also, past
history, as stored in a data base, such as data base 401, FIG. 4, can be
used to characterize a particular new signature. Signatures arriving
before and after a particular signature change can also be sued to
characterize the change.

[0033]FIG. 4 illustrates one embodiment 40 of an alert processing system.
As discussed, change in signature signal 41 is provided to radio
interface 42. This input signal is determined primarily from the spatial
signatures of the radios. The message contents of signal 41 will include
the input signal as well as perhaps one or more of the following: the
radio ID, updated spatial signature, time stamp, etc. When signal 41
arrives radio interface 42 sends all or part of the signal to
surveillance processor 43 to determine what action, if any, should be
taken. Processor 43 can operate in conjunction with one or more other
devices, via GUI interface 46 and/or other device interface 47, to help
determine the proper action. For example, it may be necessary to
incorporate inputs from other sensors, or from other surveillance
channels, or from human operators to help determine what the change in
spatial signature means. When that action is determined, external
interface 44 sends control signals to the necessary locations and/or
devices to initiate the action desired.

[0034]Assuming the radios are installed and fully operational, processor
43 uses information all of the information available to it from the
various sources. It is possible to construct, either by modeling or by
actual recording, signatures and signature patterns, that are
representative of certain occurrences. For example, a person moving
across a space will result in a certain signature pattern that can be
stored. Then, when that same signature pattern is later detected, the
system can make a determination that the signature change(s) being
detected is most likely a person or persons moving across the space.

[0035]FIG. 5 illustrates one embodiment of a GUI for radio grouping. The
purpose of the grouping is to allow an operator, or the processor, to
identify the surveillance area or sub-area where the signature change has
been detected. Areas can be established for a wide variety of purposes.
For example, a super secure area should not be grouped with an area that
does not require the same security functionality. In one mode of
operation, the operator, enters into the system the location identity for
A1, A2 . . . etc., as displayed from processor 43. This then allows the
operator to identify the physical location from which the signature
change has occurred. Alternately, the operator could select an area for
surveillance and direct radios to be broadcast to each other through that
area to see if signature changes are currently occurring in that area.
The current signature change pattern can be compared to previous
signature change patterns using a specific time of day, day of week, day
of year, etc., method or using a statistical model or any other model to
determine if a problem exists.

[0036]In this embodiment the operator could also enter location and
identity information for each radio (e.g., for correlation, maintenance,
replacement, etc.). Once the location and identity details have been
entered, grouping can be used to define which radio is in which real
group, virtual group, or sub-group thereof, for example. In this
embodiment the next step allows the operator to define the alert security
classification. While this aspect does not impact the radios, it may be
important for the radio surveillance system to know what alert action
should be executed when an alert has occurred.

[0037]FIG. 6 shows one embodiment 60 for defining the alert action. For
example, FIG. 6 shows that Severity 1 is the highest alert level meant
for evacuating the building, automatically dialing 911 with predefined
voice commands, sending other messages (e.g., voice, video, email, pager,
etc.), and executing other commands (e.g., elevator shutdown). The
operator should be able to define the actions for each class of alert
levels. Once this is done, the alert processing station would have the
capability of turning on any external system to produce the right alert
signals.

[0038]FIG. 7 illustrates one embodiment 70 of an operator interface for an
alert setting in which the GUI can be used to establish what alert level
should be reported when the radio surveillance detects a particular EMP
change. Using the GUI, any alert can be initiated from a particular
event. "Trigger Threshold" (shown in column 704) could include a list of
all possible reports from the radio surveillance system. The report could
be a signature change from a single radio set. In such a situation, any
change in the signature would trigger an output action. Or the report
could require multiple changes from a single radio set or from multiple
radio sets. Or the report could be one signature change and no further
change (change and stay). Or the report could require that the signature
change only for a short time and then revert back to the same signature
as before the change (change and change-back) etc.

[0039]Example 1, Assume A1 (column 701) is a restricted area. Assume also
that the operator is monitoring video surveillance at all times. The
optional settings for the operator are:

[0040]Option 1: Select A1, Severity 1 (column 702), all the time (column
703) and single EMP change (column 704). With this setting, the operator
would receive an alert every time there is an EMP change. This alert
option would allow the operator to only monitor the video screen(s) when
the alert is activated. Additionally, each alert can be time stamped to
simplify play back searches. This setting works well if EMP changes are
infrequent.

[0041]Option 2: Select A1, in a defined period, and single EMP change and
select A2, Alert 1, all the time and single EMP change. (A2 could be, for
example, the entrance and exit area of A1.) With this setting, the
frequency of alerts would be reduced, because it provides alerts only
when an object is moving in and/or out of the entrance and exit area.

[0042]Example 2 is for an area with variable severity classification based
on times and dates, such as may be found at a typical office, This
setting is the same as example 1, but the differences are the
classification changes with time and dates.

[0043]FIG. 8 shows one embodiment 80 of a flow chart of system operation.
As shown, process 801 determines in any of a number of ways if the
electromagnetic propagation between communicating radios has changed.
This determination can be made, for example, if the spatial signature has
changed as discussed above. If there is a change, process 802 determines
if the conditions surrounding the detected change need to be further
analyzed. For example, in some applications any change for any reason is
enough to cause a signal to be sent outside the radio system to, for
example, a surveillance system.

[0044]In other situations it may be desirable to go into more depth to
determine factors surrounding the change or to examine the magnitude of
the change. In such situations not all changes are treated equally. If
process 802 determines that further analysis is not necessary, then
process 803 sends a trigger signal to a device or location for use by
that device or location to take some action based on the detected EMP
change.

[0045]If, however, further processing is required, then process 804
performs this analysis according to guidelines established by a user.
This further analysis could be as simple or as complex as desired and
could be based on: expected changes, unexpected changes, time of
occurrence, statistics compiled over a period of time with respect to
other recorded changes, patterns put into the database by the user, etc.
Process 805 then determines, based on the detailed analysis of the EMP
change(s) if they are significant. In this context, significant means
that some action is to be taken. If so, then process 806 determines what
the proper course of action should be, based upon a set of
pre-established guidelines as discussed above and process 807 then sends
the proper signal(s) to trigger the response.

[0046]In some cases, the response is simply that an operator is alerted
that something may be wrong. In other situations, the response could be a
rearrangement of radio communications "looking" for specific additional
information, either from the radio communications or from some other
surveillance function.

[0047]Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing from
the spirit and scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be
limited to the particular embodiments of the process, machine,
manufacture, composition of matter, means, methods and steps described in
the specification. As one of ordinary skill in the art will readily
appreciate from the disclosure of the present invention, processes,
machines, manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform substantially
the same function or achieve substantially the same result as the
corresponding embodiments described herein may be utilized according to
the present invention. Accordingly, the appended claims are intended to
include within their scope such processes, machines, manufacture,
compositions of matter, means, methods, or steps.